An improved synthesis of (S)-ketamine (esketamine) has been developed, which was cost-effective, and the undesired isomer could be recovered by racemization. Critical process parameters of each step were identified as well as the process-related impurities. The formation mechanisms and control strategies of most impurities were first discussed. Moreover, the (S)-ketamine tartrate is a dihydrate, which was disclosed for the first time. The practicable racemization catalyzed by aluminum chloride was carried out in quantitative yield with 99% purity. The ICH-grade quality (S)-ketamine hydrochloride was obtained in 51.1% overall yield (14.0% without racemization) by chiral resolution with three times recycling of the mother liquors. The robust process of esketamine could be industrially scalable.

中文翻译：

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氯胺酮的工艺研究和杂质控制策略

已经开发了一种改进的（S）-氯胺酮（esketamine）合成方法，该方法成本效益高，不需要的异构体可通过外消旋作用回收。确定每个步骤的关键工艺参数以及与工艺相关的杂质。首先讨论了大多数杂质的形成机理和控制策略。此外，（S）-酒石酸氯胺酮是二水合物，这是首次公开。由氯化铝催化的可行外消旋以定量收率进行，纯度为99％。ICH级质量（S通过手性拆分和三倍的母液回收率，可得到5-氯胺酮盐酸盐，总产率为51.1％（无外消旋作用为14.0％）。氯胺酮的稳健工艺可以在工业上推广。